Hi,
I cant offer any help re discs, but why do you want to change, a set of drums in good working order will work well, I dont think discs will stop you any quicker - though a servo will help, you wont have to press as hard, the stopping power is the same. Now you'll need to adjust the brakes every so often, discs are self adjusting, but it's probably a lot cheaper to get your stock drum brakes working properly, than have to replace all with discs, calipers, hoses, master cylinders, adaptors etc...
Mine are stock, perfectly happy, MOT man always surprised with the stopping force anyway. Nowt wrong with drums, you just have to push, no servo, though you could retro fit a servo, that'd be pretty good.
Now if you are fitting a big engine, you'll be changing to bigger discs, vented etc, and then suspension, and then, and then, and so on......!
Just my 2 pence/cent/drackma.groat etc...
Cheers,
Alistair